public interface OptionalFactory extends Factory
Such factories often need some external resources. For example the default EPSG factory need a MS-Access database installed on the client machine. This database is not bundle in Geotools distribution; if the user have not installed it, the factory can't work.
This interface is not a manager for automatic download of external resources.
It is just a way to tell to
FactoryFinder that this factory exists, but can't do its job
for whatever reasons (usually a missing resource that the user shall download and install
FactoryFinder has to choose an other factory. In other words, the
OptionalFactory interface is used as a filter, nothing else. The process is as follows:
FactoryRegistry.getServiceProvider(java.lang.Class<T>, javax.imageio.spi.ServiceRegistry.Filter, org.geotools.util.factory.Hints, org.geotools.util.factory.Hints.Key)is invoked, it starts to iterate over all registered factories. If an ordering is set, it is taken in account for the iteration order.
isAvailable()is invoked. If it returns
true, then this optional factory is processed like any other factories. Otherwise it is ignored.
OptionalFactory is not designed for factories with intermittent
state (i.e. return value of
isAvailable() varying in an unpredictable way). The behavior
is undetermined if the
isAvailable() state changes with time.
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